1. Field of the Invention
The present invention relates to a cathode end plate and a breathable fuel cell stack incorporating the cathode end plate.
2. Discussion of Related Art
A fuel cell is defined as a cell for generating direct current by converting the chemical energy of fuel into electrical energy. Fuel cells create little environmental pollution and have a high efficiency because fuel and air are supplied from the outside to continuously generate electricity, unlike a conventional cell. Also, since fuel cells continuously generate electricity by means of a chemical reaction rather than combustion of energy sources such as petroleum energy, natural gas and methanol, fuel cells have been highlighted as the future in energy generation.
Fuel cells can be classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte type fuel cells, alkaline fuel cells, and others based on the electrolytes used. Each type of fuel cell varies based on fuels used, operating temperatures, catalysts and electrolytes, but generally operates by the same basic principles.
The basic concept of the fuel cell can be explained by the movement of electrons generated by chemical reaction of oxygen and hydrogen. Hydrogen is supplied to an anode electrode, and oxygen is supplied to a cathode electrode. After protons generated from the anode electrode pass through an electrolyte membrane and move to the cathode electrode, they electro-chemically react with the oxygen to generate water. Electrons generated from the anode electrode move to the cathode electrode through an external conductor to generate electricity. Also, heat is generated by the electro-chemical reaction of the anode electrode and the cathode electrode. Direct current from, for example, a direct current electromotor, can be used as the power or it can be converted into indirect current by means of an inverter. The heat generated from the fuel cell generates vapor for reformation or is used for cooling and heating, and otherwise, is discharged as heat.
The following reaction equation 1 represents the overall reaction of the operating principle of the fuel cell.Anode: H2→2H++2e−Cathode: 1/2O2+2H++2e−→H2OOverall: H2+1/2O2→H2O+Current+Heat  [Reaction Equation 1]
Fuel cell stacks can be classified as passive type stacks and active type stacks. In the passive type fuel cell system, air is supplied through natural convection while in the active type fuel cell system, air is forcibly supplied to the stack using an air supply such as an air compressor, an air pump, or the like.
“A plurality of unit cells are generally provided in a stacked arrangement compressed together to form a stack.” In the passive type fuel cell system, unit cells are planar, thereby occupying a larger area and making uniform compression of the unit fuel cells difficult. When the compression is not uniform, debris may infiltrate the fuel cell stack or material inside the fuel cell stack may leak, interfering with the effective operation of the fuel cell.
A uniform compression may be achieved when the end plate of the fuel cell stack is relatively thick. However, since the fuel cell stack often involves devices that are relatively thin and small so they can be used in mobile equipment such as a notebook computer, a personal digital assistant (PDA), a portable multimedia player (PMP), or a cellular phone, for example, limitations exist on the thickness of the end plate, and of the fuel cell in general.